It is well known in the art that Internet service can be provided over an integrated services digital network (ISDN) line. One such service utilizes multilink point-to-point protocol (MLPPP). MLPPP has been used to bond the two ISDN B-channels to provide Internet service at 128 Kbps. In addition, there is a proposal to allow the D-channel of an ISDN line to be bonded to the two B-channels, thus providing Internet service at approximately 144 Kbps. However, this proposal suffers from several drawbacks.
First, because the Internet protocol (IP) traffic is divided only according to available bandwidth, without regard for the type of application in which the packet is going to be used at its destination, packets for continuous media applications, e.g., audio or video, may wind up being transmitted over the D-channel. As is well known, the D-channel is a packet switched data channel, and so it has unpredictable delays. Consequently, it is unknown when a packet that is sent over the D-channel will arrive at its destination.
When using MLPPP for Internet service, all the packets must be reordered upon receipt at the first IP access server, e.g., a gateway or a router, to the order in which they were transmitted. Since some of packets that require reordering may have been sent over the D-channel, and this may have resulted in a significant delay, the release of packets that were transmitted and received over the B-channel may be correspondingly delayed while awaiting for the arrival of a D-channel packet that precedes them in order. Thus, the delay of the D-channel causes delays in the B-channel. In other words, packets sent over the D-channel may hold packets sent over the B-channel "hostage".
As a result of such delays, continuous media applications may suffer from poor performance. Also, for continuous media applications, the buffer requirements at the access server is increased because the packets from the B-channel must be stored until any preceding packets from the D-channel arrives.
Second, because packets over the D-channel used with MLPPP are in the well known X.25 format, the information transmitted is preceded by several different protocol layer packet headers. Thus, the use of MLPPP and X.25 introduce unnecessary complexity, while reducing the effective bandwidth available for information transfer.